Such angle-measurement systems may be used for measuring rotary motions and rotational positions of a machine part, e.g., a shaft. The rotary motion is determined either incrementally or absolutely. The output measured value is, for example, a sequence of counting pulses, a counter value or a code word. Corresponding angle-measurement systems may be used in so-called pick-and-place machines in the manufacture of electronic components, or in machine tools for measuring rotary movements. The precise reproducibility or repeatability of the rotational angles of machine parts to only a few angular seconds may be very important when working with pick-and-place machines, for example. The absolute accuracy of the measuring results of an angle-measurement system may be crucial in the case of machine tools, in particular. Angle-measurement systems may be designed such that they have no individual mounting of the components rotatable relative to each other.
The precision of an angle measurement is influenced, for example, by the quality of the angle scaling, the eccentricity of the angle scaling with respect to the mounting and by the radial eccentricity of the mounting. Particularly in the case of angle-measurement systems without self-mounting, deviations may be expected because of assembly deviations which are too great.
German Published Patent Application No. 100 19 499 describes a method for producing an angle scaling for an angle-measurement system in which the eccentricity of the body onto which the angle scaling is to be applied is measured. A correction is then made depending on the measuring results, so that a corrected angle scaling is applied.
This method may be relatively costly, and subsequently, a direct mounting on a machine part whose angular position is to be determined may be virtually impossible.
PCT International Published Patent Application No. WO 2004/008076 describes a device featuring an intermediate ring for mounting a body having an angle scaling. In this device, exact mounting of the body having the angle scaling may be comparatively difficult and costly.
European Published Patent Application No. 0 913 669 describes centering methods in which, when mounting the body having the angle scaling, the body should self-center by spring elements. The precision of the centering when working with these systems is determined by the reproducibility of the spring excursions. However, depending on the material of the spring element, the exact repeatability of the spring excursions may be unfavorably influenced, for example, in response to temperature fluctuations.
The bodies having the angle scaling inevitably exhibit circularity deviations, conditioned by manufacturing. In conventional methods, these circularity deviations are frequently recorded at many test points along the outer contour of the body. Thereupon, the midpoint of the circle of least deviation squares is calculated. To apply the angle scaling, the body is aligned so that this calculated midpoint comes to rest as precisely as possible on the axis of rotation of the support device. This type of alignment and mounting may be comparatively difficult and costly. During the later mounting of the body, provided with the angle scaling, on a machine part, the specified midpoint has to be centered again in a complex operation, precisely on the axis of rotation of the machine part in question. Since, for example, due to improved scanning techniques and interpolation electronics, such angle-measurement systems in principle allow increasingly precise measurements, the installation tolerances have to be reduced in order to exhaust the potential of the angle-measurement systems. Therefore, to increase the centering accuracy, the accuracy in determining the midpoint of the circle of least deviation squares is continually increased by increasing the number of test points, which in turn, however, increases the expenditure for manufacturing and mounting.